It seems pretty straight forward. A class 2 card is 2MB/sec a class 4 card is 4MB/s. Armed with this info, I go out today tobuy my SDHC card. What I come home with confuses me.

I got a Lexar 4GB SDHC card. http://store.lexar.com/?category=21&amp;...d=SD4GB-60-709Now it is labeled as a class 4 card (4 with that c around it) yet it says 60X with 9MB/sec write. If this card is can do 9MB/sec wouldnt this be like a class 9 card ? Why is it still labeled as class 4?

Seems there is some flaws still with the class "standards", or at least my understanding of them.

The Speed Class for SD cards is the guaranteed minimum transfer speeds. The specification of, for instance, "9MB/sec" is the maximum transfer speed. The difference is that when you're shooting video, in order to shoot an ininterupted vieo stream, it is the minimum transfer speed that matters.

Actually, there are only 3 classes: Class 2, Class 4, and Class 6. A better question might be why it isn't a Class 6 card.

The SD Association SD Card CLasses are determined by tests established by the SD Association , whereas Lexar's speed ratings are determined by tests established by Lexar. I beleive the difference is probably a direct result of the different methods used to test the cards.

Seems very flawed too me. Kind of like saying in 1920 that, "hey, we are going to have 3 classifaction ofcars. A can go 50 MPH, B can go 75 MPH and C can go 100 MPH" (no need to go higher than 100 MPH right?)

I think cards are already showing they are running better than class 6.

I think cards are already showing they are running better than class 6.

The manufacturers say their cards are fast, but when subjected to the SD Association's test, they aren't. That's why a card that Lexar says can transfer data at 9MBps is only a Class 4 card. The tests aren't outdated; they just disagree, and the most stringent of the two tests is the one I recommend you base your purchasing decision on.

The cards aren't running better than Class 6. The manufacturers are just quoting specs that make their own products look good.

When Company A says it's products are reliable, but Consumer Reports says they're not, who do you believe?

Hi there,
It is an old thread - but is best I've found so far.
I've purchased Canon PowerShot SH1 IS last week choosing over SX10 because of its full HD video.
The shop recommended card with a purchase was SanDisk Ultra II 4GB, and I bumped it up to 16GB one.
I used the camera so far mostly for photos, that's the reason I did not buy HD camcorder, but I did a couple of HD video tests.
It is of course some learning curve, correct use of IS etc., but I became suspicious of SD card performance and I have had another look.
To my big surprise SanDisk Ultra II 16 GB I bought is Class 2 card only! :evil:
The shop I bought everything downplays the importance of Class 2 rating and justifies the performance, or lack thereof, to Canon itself saying that it not really HD camcorder.:P
To this I can only laugh, but I was honest enough to admit that I did not do all the tests (most importantly with various IS setting) and additionally compare them to my another SanDisk SDHC, this time Extreme III which is Class 6 to make sure it is problem of SanDisk Ultra II 16 GB Class 2. So we agreed that I would test for another week, and then we'll see.
At that moment I was more negative about the shop, but further investigation shows that SanDisk is far from innocent.
I own a number of SanDisk SDHC cards, and another SanDisk Ultra II (8 GB) is Class 4?:?
Searching the net I've found a number of references (or rather pictures) to both Class 2 and Class 4 SanDisk Ultra II 16 GB, even if SanDisk declared speed is the same:15 MB/s!
I am writing this to warn others because if I've know before what I know now I would be much more careful.
I've trusted SanDisk before and this trust has blinded me. Not the first time, and alas probably not the last, but what surprised me is missing more information about this on the net. This thread is the only so far being spefic about Lexar cards, and I wanted to add SanDisk to the list.:evil:
Caveat emptor – double check speed ratings.
Tx
Rgds
Fila